In 1990, there were over 1.69 million noninstitutionalized walker users in the United States (85% over the age of 65 years). A walker is used to provide support, reduce weight bearing on the lower limbs, and therefore to minimize the likelihood of falls. There were, however, over 118.000 accidents (>75% involving females) reported between 1987 and 1992 which involved walker use and which required emergency room treatment (mostly hip fractures and upper body trauma). Biomechanical movement analysis is a key tool for understanding walker-assisted gait, and for providing quantitative objective measures of performance leading, optimistically, to improvement in walker design and guidance in walker use. Biomechanical analyses that include the kinetics of gait (e.g. force, moments and mechanical energy transfers) may be the most important tools because they help to explain the kinematics, and may reveal the neuromuscular strategy underlying the movement. To date, commercial gait analysis software do not incorporate Assistive devices (like a walker) into the Inverse Dynamics calculations because, in part, instrumented walkers that provide a complete description of the constraint provided by the walker handle do not exist commercially. The instrumented walker manufactured by AMT uses a 6 degree of freedom load cell attached to the handle to record the constraint force provided by the handle (the reaction force at the hand-handle interface). In order to perform an inverse dynamics analysis it is necessary to have 9 variables to define the reaction force completely (e.g. Force Vector (Fx, Fy, Fz), Center of Pressure (CPx, CPy, CPz), and Free Moments (Tx, Ty,Tz)) In Phase I AMTI will add two sets of 8 strain gauges to a new central core on the walker handle to provide signals for two components of the couple applied to the handle. C-Motion will use the eight signals, plus the geometry of the handle, to define completely the constraint force at the hands. C-Motion will develop an algorithm, based on the 6 degree of freedom analysis in its Visual3D software, that uses the 9 signals, and motion capture data of the position and orientation of the walker handles and the subject's hands, to produce a complete inverse dynamics analysis of the upper arms during walker assisted gait.